Piezoresistive Carbon Nanofiber-Based Cilia-Inspired Flow Sensor

Abstract

Evolving over millions of years, hair-like natural flow sensors called cilia, which are found in fish, crickets, spiders, and inner ear cochlea, have achieved high resolution and sensitivity in flow sensing. In the pursuit of achieving such exceptional flow sensing performance in artificial sensors, researchers in the past have attempted to mimic the material, morphological, and functional properties of biological cilia sensors, to develop MEMS-based artificial cilia flow sensors. However, the fabrication of bio-inspired artificial cilia sensors involves complex and cumbersome micromachining techniques that lay constraints on the choice of materials, and prolongs the time taken to research, design, and fabricate new and novel designs, subsequently increasing the time-to-market. In this work, we establish a novel process flow for fabricating inexpensive, yet highly sensitive, cilia-inspired flow sensors. The artificial cilia flow sensor presented here, features a cilia-inspired high-aspect-ratio titanium pillar on an electrospun carbon nanofiber (CNF) sensing membrane. Tip displacement response calibration experiments conducted on the artificial cilia flow sensor demonstrated a lower detection threshold of 50 µm. Furthermore, flow calibration experiments conducted on the sensor revealed a steady-state airflow sensitivity of 6.16 mV/(m s−1) and an oscillatory flow sensitivity of 26 mV/(m s−1), with a lower detection threshold limit of 12.1 mm/s in the case of oscillatory flows. The flow sensing calibration experiments establish the feasibility of the proposed method for developing inexpensive, yet sensitive, flow sensors; which will be useful for applications involving precise flow monitoring in microfluidic devices, precise air/oxygen intake monitoring for hypoxic patients, and other biomedical devices tailored for intravenous drip/urine flow monitoring. In addition, this work also establishes the applicability of CNFs as novel sensing elements in MEMS devices and flexible sensors.

Flexible Graphene-on-PDMS Sensor for Human Motion Monitoring Applications

“…2 (a) shows the interface of the top and bottom PDMS layers with the graphene nanoflakes confirming the binding of the polymer substrate with the nanoflakes percolation network. The piezoresistive strainsensing mechanism in the graphene-PDMS sensor can be attributed to the conductive domain disconnection mechanism reported previously in other similar nanomaterial-polymer composite based sensors [3], [5], [9]. The SEM micrograph in Fig.…”

“…Thus, flexible and stretchable sensors utilizing piezoresistive property of nanomaterial-polymer composites has been a growing area of research for the last two decades. Nanomaterials such as carbon nanotubes (CNTs) [2], carbon nanofibers (CNFs) [3]- [5], silver nanowires [6], carbon black [7], [8], and graphene [9], [10] have been employed as piezoresistive sensing elements in many of the works reported in the past. Also, in most of those nanomaterial-polymer composite-based sensors, elastomers like polydimethylsiloxane (PDMS), ecoflex, and rubber have been the materials of choice mainly because of their superior flexibility, stretchability, and excellent response to torsion [11]- [13].…”

Biomimetic Ultraflexible Piezoresistive Flow Sensor Based on Graphene Nanosheets and PVA Hydrogel

“…Researchers aim to reach a trade-off between these two variables. Recently, Sengupta and Trap [24] developed a piezoresistive flow sensor made of carbon nanofiber (CNF) as a sensing membrane and a high-aspect-ratio titanium pillar as a stimulation factor. They demonstrated high sensitivity for steady-state airflow and oscillatory water flow.…”

Transport and mixing by metachronal waves in nonreciprocal soft robotic pneumatic artificial cilia at low Reynolds numbers

“…The major topics include fluid transport and mixing, 6,27,[33][34][35][36][37][38][39][40][41][42][43][44][45][46] particle/ droplet manipulation, 24,[47][48][49][50] and artificial cilia as sensors and robots. [51][52][53][54][55][56][57] Using numerical simulations, one can study the motion and fluid propulsion of systems from one single cilium to large ciliary arrays. Many experimental studies focus on mimicking the asymmetric motion of the individual cilia, consisting of an effective and a recovery stroke, 3,4,7,33,58 and a few on creating metachronal waves of cilia arrays.…”